1. Field of the Invention
The present invention relates to a method for keeping a body surface free of scale, fouling and any other kind of dirty generated by the adherence of in-water living organisms, such as marine life, such surface being in contact with water. The invention also relates to a sound wave generating assembly for the same purposes of the above referred method. Although the present method and assembly are preferably applied to hulls of vessels and boats, and although this specification relates to such vessels and boats, those references are just given as examples while the invention may be applied to any body in contact with water, such as floating supports for bridges, sheet protective barriers, marine oil platforms, marine oil pipes, general piping and all bodies that are temporarily or permanently in contact with water.
The problem which affects the hull of a vessel and particularly the bottom thereof, that is the portion of the hull under water surface, involves enormous economic and financial looses to the naval industry, naval trade companies and insurance companies. A basic problem is that the surveys along the life of the vessel are directly related to the conditions of operation of the hull, thus when the hull is so damaged to an extent that its structural features are generally deteriorated, the hull, economically speaking, is impossible to be repaired whereby the vessel is out of service and scrapped or wasted.
The hull is damaged by different agents, such as physical agents, chemical agents and biological agents. The physical agents are elements that impinges on the hull or bottom thereof and generate a direct damage. Thus the protective layer or covers the hull such as paints are removed and the material of the hull, i.e. steel, is exposed to be in direct contact with water. If the water is salt water the steel is energically attacked. The chemical agents particularly act in such places where the physical agents have removed or damaged the protective covers. Although in the remaining parts of the hull the chemical agents also act, they take more time to reach to the steel after the protective covers have been damaged. In such places the hull becomes rusty and the steel plates thereof must be replaced. Finally, the biological agents, microscopic or macroscopic, generate scale, fouling and barnacles adhered to the hull, chemically and mechanically affecting the hull, which effects are the most important generated by living agents having a large biological activity. From the mechanical point of view, the weight of the vessel is increased by enormous quantity of this kind or organisms and, in addition, the navigability conditions are directly affected because of the increasing of the frictional resistance generated by the irregular surface of the fouling, directly leading to the lost of speed of the vessel.
While the physical processes are contingent, like a collision, and the chemical processes act in particular conditions such as aging of the protective covers or after the first action of the physical agents, the biological agents start to act immediately after the vessel is launched and act steadily and continuously. Additionally, the action of the biological agents leads to and accelerates the above referred chemical process because they generate micro fissures of clefts in the paint layers, thus allowing the sea water to enter in contact with the hull steel and chemically acting on it generating oxidation that damages the steel. Thus, the biological processes are very important. In order to set an example of the steps of the oxidity process on the hull and its relationship with the biological agents, it may be useful to see that the iron oxidation (rust) involves the following four steps:
(1) Fe.sub.(s) - - - Fe.sup.+2 +2e.sup.- PA0 (2) e.sup.- +H - - - H PA0 (3) 4H+O.sub.2(g) - - - 2H.sub.2 O PA0 (4) 4Fe.sup.2+ +O.sub.2(g) +(4.2%)H.sub.2 O - - - 2(Fe.sub.2 O.sub.3 .multidot.xH.sub.2 O).sub.(s) +8H.sub.+
H being provided by the water or acids of the organisms adhering mechanisms.
wherein 2(Fe.sub.2 O.sub.3 .multidot.xH.sub.2 O).sub.(s) is rust and 8H.sub.+ accelerates the reaction of formulae (2).
The net reaction, considering the four steps, is: EQU 4Fe.sub.(s) +3O.sub.2(g) +2xH.sub.2 O - - - 2(Fe.sub.2 O.sub.3 .multidot.xH.sub.2 O).sub.(s)
The existence of biological acids, either produced by some of the adhering mechanisms of the agents or existing as natural elements of the metabolism of the agents, accelerates the second step of the oxidation equation by capturing the electrones released by the mutual iron on its hydrogen cations (H). The altered or broken paint layer that allowed the beginning of the reaction, plus the layer of rust that accelerates the second step of the above formulae when producing hydrogen cations, plus the scale layer plus the fact that all is in an aerobic medium, should operate as a barrier to the gaseous oxigen necessary for the third step of the above equation and therefore the process should be stopped. However the process does not stop because the metabolism of the algae, either unicellular or pluricellular organisms, (due to the biochemical process of photosynthesis) forms and releases gaseous oxigen in the medium, which accelerates the first step of the equation increasing thus the oxidative process.
Considering the damages that the three above mentioned agents make in the vessels, all the countries as well as naval insurances and registers have established that a vessel must be registered, periodically revised, controlled and cleaned in order that the hull be in operative conditions.
To take an idea of the financial and economical consequences of the lost of speed and the need of periodical cleanings of the hulls, it may be interesting to see that in 1980 the mercantile marine of the world consisted of 420 millions of tons and the navy had 150 millions of tons, 175 millions of tons corresponding to oil transporting ships.
The above figures remark the great importance of the damages caused by the above cited agents in the vessel hull and they give an idea of the enormous quantity of square meters of hulls which should be cleaned annually.
With reference to marine oil platforms and to give an idea of the importance of the above phenomenom, it may be said that in the North Sea there are more than 150 platforms and more than 6,000 kilometers of piping, the cleaning and maintenance thereof involving very high costs.
Prior to enter into the concept of the present invention, the applicant feels necessary to first describe the complex interaction existing between the biological agents, the special characteristics of the medium wherein these agents live, its differences with other known medium, and a syntactic classification of the several groups of agents which accelerate the damaging of a ship and other bodies (metallic or not) in contact with water.
The big difference between the sea environment and the ground or soil environment is that in the sea the scientific variables thereof are restricted to short ranges, while the living ranges for conditions in the ground are wider. The sea environment is more stable because its thermal variations are lower and its changes are slow due to the regulating features of the water; the salt concentration is constant, only varying the kind of ions (3.5% of concentration except the Dead Sea with a concentration of about 25%); the aqueous medium has the same osmotic pressure that the protoplasm of the organisms cells; this is why the membranes of these organisms do not suffer the pressures to which the organisms living on the ground are subject (mechanical action); the water density is uniform and not variable while the marine life is not adapted to changes. These and other reasons make the marine environment a very stable environment and the life living in this medium is adapted to this stability. Therefore the tolerance limits for life are very restricted and, because life is adapted to such conditions they are extremely sensitive to any change in the environment. An example of this is the sensitivity of the microflora and the macroflora as well as the micro and macrofauna to any contaminant which, although with a lower concentration, leads to the immediate dead thereof.
A biological community live in a limited zone or "habitat" which may be extended or reduced. One of the most important principles of the ecology is that animals and vegetals live all together in armonic arrangement, without being randomly spreaded all over the earth surface. All new zones (i.e. a just launched ship) will receive the establishing of a methodical succession of communities, with change their state and leas to a mature and stable community, namely a top community. The series are so regular that an ecologist, when studying the community may foresee the succession of future changes.
The ocean is a big reserve of nutritive elements which are essential for the beings living therein as well as in the ground. It is evident that the total weight of the organisms living in the ocean (biomasa) exceeds the weight of all the beings living on the ground and sweet waters.
Because of the seas are communicated to each other, the sea life has no limits but just limited by factors like temperature, salinity (kind of ions) and depths.
The sea may be divided into regions characterized by different physical conditions and, therefore, regions inhabited by specific classes of animals and vegetals; thus there is a "continental bank" extended along a uniform distance from the seashore and the depth thereof slowly and gradually increases, then, there is a continental "barrier" and finally there is the "abyssal depth". The region of shallow waters in the continental bank is called "neritic zone". The high sea that is out of the continental bank is the oceanic zone. The superficial portion of water wherein the sunligth penetrates to allow photosynthesis in the life development is called "eufotic zone", the lower limit thereof varying between hundred to two hundred meters depending on the water clarity. The region under the sufotic zone is called "batipelagic", extended up to a depth of two thousand meters while under this zone the region is called abism, the depth thereof exceeding ten thousand meters.
The neritic zone may be divided into the high tide zone, the intermediate zone and the low tide zone. The tide zone, one of the most favourable habitats, it is supposed to be the base where the life started. Water, ligth, oxigen, carbondioxide and mineral salts are extremely convenient for the vegetal life. Full of vegetal life, this zone is a good shelter and a provision of food for any animal species. Immediately after a solid body appears in the environment, a large variety of algae can fix themselves onto the body, as well as mose, sea coralina, etc., forming a community. This is a fundamental characteristic of this medium. There exists a rivalry between the vegetals for reaching to occupy enough space and between the animals for food. The limit for the development of the species is the limited space wherein the growth may be fixed and settled. All the biological potential of the sufotic zone in the high sea remains intact because of the lack of points wherein the organisms can fix, however the macroflora can not develope.
Within the microscopic world there are protozoans like phoraminipherals and radiolareans, little crustaceous and larvas for many species.
No reference to superior animals will be made because of the lack of importance thereof in connection with the present invention. Sweet water such as lakes and moving waters such as rivers have biological communities which are more know than the sea communities and generally, although they are different communities they have common phylum and the ecological behavior thereof is similar, particularly to connection with the colonization mechanisms or the capacity of adapting to a body or area in the environmental equilibrium. In order to understand the diversity and complexity of the biological agents a synthetic classification will be given, particularly referring to certain phylum of big importance because of the number of members and generic existence in all the seas:
______________________________________ Some Flagellata PROTISTAS Mosses Bacterium Blue-green (2500 sps) Green (5000 sps) Brown-golden phylum: crysophyta (diatom) VEGETAL phylum: KINGDOM Algae pirrophyta (diniflagellata) Brown (1000 sps) phylum: phaeophyta Red phylum: rhodophyta ______________________________________